This invention relates to an operation microscope of small working distance, intended particularly for operations in narrow and deep operation channels.
Operation microscopes are stereomicroscopes which are held in suitable manner on supporting arms and couplings for microsurgical operations. In order that the surgeon shall not be impeded by the microscope in the guidance of his microsurgical instruments, a minimum free working distance is necessary from the front surface of the operation microscope to the operation field. Depending on the specialty and the operation to be effected, the working distance is between 100 and 400 mm. For undisturbed observation and illumination, a relatively large conical region within which the ray paths extend must be kept free in front of the objective.
For operations in narrow and deep operation channels such as are a matter of course, for instance, in microsurgery on the vocal cords or on intervertebral disks, it may, however, happen that the illuminating ray path is in part cut off in the operation channel and by reason of the microsurgical instruments introduced therein. As a result, available illumination in the operating area is reduced. Of much greater importance, however, is the fact that both observation ray paths may be partly blocked; and in the extreme case, only a single observation ray path can be used. Such circumstances handicap the surgeon by eliminating one of his most important prerequisites, namely, sufficiently good stereo observation, for location of depth in the operating area and for proper guidance of microsurgical instruments.
A radial reduction in size of the illuminating or observation cone by increase of the working distance is generally not possible (1) due to the reduction in the angle of convergence inherent therein, which angle should be as large as possible for the sake of good stereo observation, and (2) due to the characteristically rather low aperture of objectives in operation microscopes.
It is known from German Provisional Patent (Auslegeschrift) No. 2,309,203 to provide a conical cover or shield for the region which is to be kept free for the ray path. This purely mechanical measure, to be sure, prevents cutting off of the ray paths by surgical instruments but nevertheless does not increase the space available for manipulation. An objective provided with such a cover is not suitable for introduction into long cylindrical openings. Further, what has been stated above with respect to the angle of convergence and low aperture also applies.
In general, rigid or flexible endoscopes are used for microscopic observations in deep or narrow body openings. However, relatively few endoscopes are known which permit stereoscopic observation.
German Pat. No. 2,354,370 describes such an endoscope which consists of two flexible individual endoscopes coupled by a clamp, but it is suitable only for introduction in the nostrils. U.S. Pat. No. 3,520,587 also describes a flexible stereo endoscope which contains two separate image-conducting fiber bundles in a surrounding tube.
Flexible endoscopes are, however, only poorly suited for observation of operating areas since their image quality, even in the case of very good image conductors, is fundamentally poorer than that of operation microscopes, due to the structure of the individual-fiber arrangements, and also due to split or completely broken fibers. Their advantage of flexibility is furthermore not required in operation microscopy; on the contrary, such flexibility can have a detrimental effect as a result of image instability.
A rigid endoscope for stereo photography is known from German Unexamined Patent Application (Offenlegungsschrift) No. 1,766,803 and from German Gebrauchsmuster No. 1,996,605. This instrument has an elongated base body in which two parallel optical systems are arranged, and in which the proximal end bears a stereo attachment for binocular observation or for stereo photography. The doubled design of the observation channel and the resultant additional centering work within the channel, as well as of the two channels with respect to each other, make this instrument rather expensive to manufacture.
Furthermore, all endoscopes have the disadvantage that, in accordance with their purpose, they are to be manually guided by the user, so that only one hand remains free for operating the adjustment elements and handling the surgical instruments. When a television camera or a co-observer tube is attached as is frequently the case with operation microscopes, an endoscope, for the reasons indicated above, would now be in two senses very difficult to handle.